Thermoplastics, in particular, polycarbonate resins are widely used as a structural material replacing glass due to excellent transparency, light weight, and improved impact strength. However, application of the polycarbonate resins is limited since the polycarbonate resins exhibit poor surface properties such as scratch resistance, weatherability, and chemical resistance. Therefore, there is a strong demand for improvement of the surface properties of a polycarbonate resin substrate.
As a method of improving the surface properties of a polycarbonate resin molded product, a method of coating the surface of the molded product with a surface treatment agent is known. For example, forming a cured layer of a polyfunctional acrylic photocurable resin, a melamine or organopolysiloxane thermosetting resin on the surface of a polycarbonate resin substrate has been proposed.
Of these, a polycarbonate resin coated with an organopolysiloxane is considered to be useful due to excellent scratch resistance and chemical resistance. However, since the organopolysiloxane has insufficient adhesion to the polycarbonate resin, peeling of the coating layer occurs when used outside for a long time.
As a method of improving adhesion, Patent Document 1 and the like propose mixing various polymers having excellent adhesion in a coating liquid. Mixing such a polymer may cause scratch resistance to deteriorate, and may significantly lower the weatherability of the coating liquid in some cases. Therefore, in applications where scratch resistance and weatherability are required, it is common to use a double coating method including applying an acrylic coating liquid to a polycarbonate resin substrate as a primer and providing a coating layer thereon. However, the double coating method exhibits reduced productivity due to the long working process. Therefore, development of a single coating method is awaited.
Patent Document 2 proposes a method of providing abrasion resistance and adhesion by a single coating method. In this method, it is preferable to use at least one of epoxy group-containing silane coupling agents and amino group-containing silane coupling agents. The silane coupling agent is used in an amount of 5 to 10 parts by weight for 100 parts by weight of the nonvolatile components (JIS K5401) of the coating liquid. The document describes that if the amount of the silane coupling agent is less than 5 parts by weight, film properties and adhesion may deteriorate, and if the amount of the silane coupling agent exceeds 10 parts by weight, abrasion resistance may deteriorate.
As described in Example 6 of Patent Document 2, when a polycarbonate which is not or is insufficiently provided with resistance to ultraviolet rays is used as a substrate, the resulting polycarbonate resin multilayer body may have lowered weatherability and suffers from problems such as peeling of the coating layer.
Patent Document 3 discloses a composition containing a silicone-containing polymer ultraviolet absorber and a polyorganosiloxane. However, it is impossible to obtain a stable dispersion by merely mixing a polymer ultraviolet absorber and a polyorganosiloxane.
[Patent Document 1] JP-A-7-90224
[Patent Document 2] JP-A-2000-272071
[Patent Document 3] JP-A-2004-1393
In view of the above problems, an object of the invention is to provide a transparent cured film exhibiting sufficient adhesion to a polycarbonate resin substrate without using a primer and having excellent scratch resistance and weatherability, a coating composition, and a resin multilayer body.